OFFSET
0,2
FORMULA
a(0) = 1, a(1) = 7; a(n) = ((2*n+5)*a(n-1) + 3*(n+5)*a(n-2))/n.
a(n) = (binomial(n+6,3)/20) * Sum_{k=0..floor(n/2)} binomial(n+3,n-2*k) * binomial(2*k+3,k).
a(n) = Pochhammer(n+1, 6)*hypergeom([(1-n)/2, -n/2], [4], 4)/6!. - Stefano Spezia, Jul 10 2024
MATHEMATICA
a[n_]:= Pochhammer[n+1, 6]*Hypergeometric2F1[(1-n)/2, -n/2, 4, 4]/6!; Array[a, 25, 0] (* Stefano Spezia, Jul 10 2024 *)
PROG
(PARI) a(n) = binomial(n+6, 3)/20*sum(k=0, n\2, binomial(n+3, n-2*k)*binomial(2*k+3, k));
CROSSREFS
KEYWORD
nonn
AUTHOR
Seiichi Manyama, Jul 09 2024
STATUS
approved